Hybrid Recursive Active Filtering with Adaptive Transfer Function Shaping Capability

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This invention introduces a hybrid recursive active filter that combines analog and digital technologies to deliver highly adaptable and selective electronic filtering. The system uses an analog power amplifier in the signal's forward path, while a digital feedback loop processes the output with multiple digital feedback paths—each with specific attenuation and delay—to shape the filter's response. This approach enables dynamic adjustment of filter characteristics, offering stable, reconfigurable, and efficient filtering, especially suitable for demanding RF (radio frequency) communication applications.

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• Replacing bulky and expensive RF cavity filters in wireless base stations and communication equipment (e.g., GSM, LTE, WCDMA).
• Adaptive filtering in software-defined radios (SDR) and cognitive radio systems for varied frequency standards.
• Advanced selective filtering in RF front-ends to reduce out-of-band interference and enhance performance.
• Applications in transmitters and receivers needing agile and highly customizable filter behaviors.
• Digital pre-distortion systems for transmitters requiring real-time filter adaptivity.

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• Reduces size, cost, and complexity by replacing large hardware filters with a smaller, more flexible digital/analog solution.
• Enables real-time and in-situ adaptability to different frequency bands and operating conditions (frequency-agile filtering).
• Improves selectivity, dynamic range, and steepness of the filter's response through multi-path digital feedback.
• Provides stable filter operation and easy reconfiguration via software, supporting software-defined and cognitive radio technologies.
• Enhances noise rejection and system performance by effectively controlling both passband and stopband filter behaviors.
• Facilitates the implementation in standard digital hardware (like FPGA or ASIC), enabling integration with existing digital signal processing systems.

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Patent Abstract

There is provided a technique of hybrid recursive active filtering with adaptive transfer function shaping capability. Such technique exemplarily comprise a hybrid recursive active filter, comprising analog power amplifier means in a forward path for amplifying an input signal to generate an output signal, and digital signaling processing means in a feedback loop for applying a feedback signal on the basis of the output signal on the input signal, wherein the digital signaling processing means comprises a plurality of digital feedback paths, each digital feedback path being configured to process the output signal with a path-specific attenuation and a path-specific delay, and combining means for combining processed signals from the plurality of digital feedback paths to generate the feedback signal.